Myths: Salmon and the Sea Limiting factors are all in fresh water, hence marine survival does not vary The ocean has unlimited capacity to support salmon All juveniles salmonids migrate rapidly to the north

OSU purse seining—

Ocean carrying capacity It varies –Seasonally—Coastal Upwelling –Interannually—El Niño/La Niña –Interdecadally—Pacific Decadal Oscillation –Intercentenially

1983 El Niño

Predictions for 1983 coho returns: 1.3 million vs. 600 thousand

Timing (spring transition) and intensity are both important Drifter trackstemperatureChlorophyll

Strong upwelling=good survival during cool PDO Poor correlation with upwelling during warm PDO Strong stratification

Pacific Decadal Oscillation. Warm or positive phase Cool or negative phase

OPI (hatchery) coho marine survival: PDO and stratification Why? Leading hypothesis: changes in ocean conditions impact the entire marine food-web PDO shift Strong stratification in 1990s

upwelling food webs in our coastal ocean Cool water, weak stratification subarctic high nutrients, a productive “subarctic” food-chain with abundant forage fish and few warm water predators Warm stratified ocean, few subtropical nutrients, low productivity “subtropical” food web, a lack of forage fish and abundant predators

What controls survival? Hypotheses and mechanisms Critical period during early ocean life is affected by ocean conditions Ocean productivity, prey availability and growth –Faster growth, less predation –Critical size to avoid winter starvation –Area and distribution of highly productive water Predation intensity—more big predators when warm waters intrude and close to shore